Structure-dependent Fano resonances in the infrared spectra of phonons in few-layer graphene

The in-plane optical phonons around 200?meV in few-layer graphene are investigated utilizing infrared absorption spectroscopy. The phonon spectra exhibit unusual asymmetric features characteristic of Fano resonances, which depend critically on the layer thickness and stacking order of the sample. The phonon intensities in samples with rhombohedral (ABC) stacking are significantly higher than those with Bernal (AB) stacking. These observations reflect the strong coupling between phonons and interband electronic transitions in these systems and the distinctive variation in the joint density of electronic states in samples of differing thickness and stacking order.     

On the banach spaces with the property (V *) of Pelczynski. — II

Summary We present a converse of a result contained in our paper «On the Banach spaces with the property (V^*) of Pelczynski» so obtaining a characterization of that family of Banach spaces. Hence some extensions of other results from that note are presented. At the end we study property (V^*) in spaces of operators with compact range.The results of this paper were obtained during the permanence of the author at Kent State University, Kent, Ohio 44242, U.S.A. thanks to a fellowship of the Italian C.N.R.     

On Banach spaces with the Gelfand-Phillips property. II

We present some result of lifting of the Gelfand Phillips property from Banach spacesE andF to Banach spaces of compact operators and of Bochner integrable functions. Moreover we studyC(K) spaces possessing the same property. In the last section we prove some result concerning the so called three space problem for the Gelfand Phillips property too.     

Selective Binding and Redox-Activity on Parallel G-Quadruplexes by Pegylated Naphthalene Diimide-Copper Complexes

G-quadruplexes (G4s) are higher-order supramolecular structures, biologically important in the regulation of many key processes. Among all, the recent discoveries relating to RNA-G4s, including their potential involvement as antiviral targets against COVID-19, have triggered the ever-increasing need to develop selective molecules able to interact with parallel G4s. Naphthalene diimides (NDIs) are widely exploited as G4 ligands, being able to induce and strongly stabilize these structures. Sometimes, a reversible NDI-G4 interaction is also associated with an irreversible one, due to the cleavage and/or modification of G4s by functional-NDIs. This is the case of NDI-Cu-DETA, a copper(II) complex able to cleave G4s in the closest proximity to the target binding site. Herein, we present two original Cu(II)-NDI complexes, inspired by NDI-Cu-DETA, differently functionalized with 2-(2-aminoethoxy)ethanol side-chains, to selectively drive redox-catalyzed activity towards parallel G4s. The selective interaction toward parallel G4 topology, controlled by the presence of 2-(2-aminoethoxy)ethanol side chains, was already firmly demonstrated by us using core-extended NDIs. In the present study, the presence of protonable moieties and the copper(II) cavity, increases the binding affinity and specificity of these two NDIs for a telomeric RNA-G4. Once defined the copper coordination relationship and binding constants by competition titrations, ability in G4 stabilization, and ROS-induced cleavage were analyzed. The propensity in the stabilization of parallel topology was highlighted for both of the new compounds HP2Cu and PE2Cu. The results obtained are particularly promising, paving the way for the development of new selective functional ligands for binding and destructuring parallel G4s.     

A new biologically active molecular scaffold: crystal structure of 7‐(3‐hydroxyphenyl)‐4‐methyl‐2H‐[1,2,4]triazolo[3,2‐c][1,2,4]triazole and selective antiproliferative activity of three isomeric triazolo–triazoles

A study of three isomeric compounds containing a phenolic moiety attached to the nitrogen‐rich triazolo–triazole bicycle is presented. In the three isomers, the phenolic OH group is in the ortho, meta and para positions. The crystal structure analysis of the meta isomer (C₁₀H₉N₅O) shows that the 2H‐tautomer is present in the crystal and that the molecule adopts a substantially planar geometry. However, the conformation found in the crystal is different compared to the monoprotonated cation of the same compound previously investigated in several salts. The packing of the meta isomer is driven by the formation of strong hydrogen bonds and shows the formation of infinite planar ribbons, parallel to a, formed around 2₁ crystallographic axes. The three isomers were tested against some cancer cell lines and also against normal cell lines. The ortho isomer shows a weak antiproliferative activity, the meta isomer shows significant antiproliferative activity against some cancer lines and no activity against healthy cell lines, and the para isomer is active against all the tested cell lines.     

Superconductivity of Rb 3 C 60 : breakdown of the Migdal-Eliashberg theory

In this paper, through an exhaustive analysis within the Migdal-Eliashberg theory, we show the incompatibility of experimental data of Rb₃C₆₀ with the basic assumptions of the standard theory of superconductivity. For different models of the electron-phonon spectral function α ² F (Ω) we solve numerically the Eliashberg equations to find which values of the electron-phonon coupling λ, of the logarithmic phonon frequency and of the Coulomb pseudopotential μ ^* reproduce the experimental data of Rb₃C₆₀. We find that the solutions are essentially independent of the particular shape of α ² F (Ω) and that, to explain the experimental data of Rb₃C₆₀, one has to resort to extremely large couplings: λ = 3.0±0.8. This results differs from the usual partial analyses reported up to now and we claim that this value exceeds the maximum allowed λ compatible with the crystal lattice stability. Moreover, we show quantitatively that the obtained values of λ and strongly violate Migdal's theorem and consequently are incompatible with the Migdal-Eliashberg theory. One has therefore to consider the generalization of the theory of superconductivity in the nonadiabatic regime to account for the experimental properties of fullerides. Received 30 March 2001     

Continuity of weak solutions to certain singular parabolic equations

Sunto Le equazioni paraboliche singolari (1.1)nella introduzione, si presentano come modelli di una classe generale di fenomeni di diffusione con cambio di fase. Le soluzioni deboli sono trovate in senso globale come classi di equivalenza in certi spazi di Sobolev. In questo lavoro si dimostra che le soluzioni deboli ammettono delle rappresentanti continue nell'interno del dominio di definizione. Si danno anche delle condizioni di continuità fino alla frontiera.

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Sponsored by the United States Army under Contract No. DAAG29-80-C-0041. This material is based upon work supported by the National Science Foundation under Grant No. MCS78-09525 A01.     

Optical conductivity of spin/lattice polarons in underdoped copper oxides

Optical and spectral properties of carriers in the presence of strong antiferromagnetic correlations and interacting with optical phonon modes are analyzed using Dynamical Mean Field Theory. We interpret the mid-infrared band in σ(ω) in term of mixed spin lattice polaronic excitations which arise from the stabilization of the lattice polaron due to the antiferromagnetic correlations. We compare our results with experimental data in NCCO showing that the doping and temperature dependences of the optical conductivity in this compound is naturally reproduced within a spin/lattice polaronic model.